1. Field of the Invention
The present invention relates to a wireless local area network (LAN). More specifically, the present invention relates to a packet transmission system in a wireless LAN.
2. Description of the Related Art
The LAN was initially developed and used as a wired network. However, following an incessant pursuit for speed-up and cost reduction of a wireless LAN as well as a development of mobile computing and mobile terminal techniques in recent years, the use of the wireless LAN configured by substituting at least a part of the wired network with a wireless network has gradually spread.
As Internet Protocol telephone (IP telephone or IPT) has spread, a voice is becoming one of important applications even in the field of the wireless LAN and cooperation of the voice application with the other applications is becoming important (see Non-Patent Literature 1).
Non-Patent Literature 1: IEEE 802.11 Standards
For an ordinary wireless LAN system according to the currently most popular IEEE802.11 Standards, however, a maximum number of simultaneous calls is only about six. The ordinary wireless LAN system cannot ensure, therefore, a sufficient number of simultaneous calls for a wireless telephone system.
The reason is as follows. In the wireless LAN at a transmission rate of 11 Mbps using a 2.4 GHz band according to the currently most popular IEEE 802.11 Standards, overhead during a packet transmission time is larger in amount, resulting in quite low transmission efficiency in transmitting a packet having a small data length such as a voice packet.
Meanwhile, a magnitude of the overhead of the packet transmission does not depend on a packet period. It is, therefore, possible to reduce an overhead ratio, improve the voice transmission efficiency, and increase the maximum number of simultaneous calls by setting the packet period longer. The longer packet period, however, causes call quality-related disadvantages including not only an increase in a delay in voice transmission but also a considerable degradation in call quality when a packet loss occurs.